Figures (1)

Hindle sphere testing of three zones of a convex hyperboloid (f/12) using three surfaces of the same diameter: (a) with a 146-cm radius of radius of curvature views the second zone; and (b) with a 190-cm radius of curvature views the second zone; and (c) with a 247-cm radius of curvature views the inner zone. (The vertical scale is expanded for the sake of clarity.)